Has anyone else did this???

For the past 3 months my periods have been irregular most of the time I've just been spotting and just lasting 4 days when they usually last 8 days or more and me and my son's dad have just got back together 4 months ago and my periods was regular before then and the first month we was together until we started having unprotected sex. I don't know what it is has anyone else did this?? I've took pregnancy test but they all say negative